A 21-year-old counselor at one of Northern California's oldest and most popular Jewish summer camps was killed Wednesday morning when a massive oak tree crashed down on the campfire circle, as hundreds of children ate breakfast in a nearby dining hall.

Investigators say it isn't clear why the trunk of the 70-foot-tall black oak broke in half at Camp Tawonga in the high Sierra. Four adult staff members were also treated at area hospitals but no campers were injured.

"There was nothing to indicate there was anything wrong with this tree," Tuolumne County Sheriff's Sgt. Jim Oliver said. "Even to look at the existing tree trunk, there is still nothing wrong. Basically, it was a freak accident, as we can tell today."

An aerial view of the camp area. (KGO)

Authorities identified Annais Rittenberg, a native of New York who attended UC Santa Cruz, as the counselor who died. A nature enthusiast, Rittenberg worked at a local radio station and majored in environmental conservation at the university, where she would have been a senior in the fall, a campus representative said.

"As our own hearts are still hurting, we send our sincerest condolences to her family and loved ones,'' the camp said in an email to parents.

PG&E annually inspects trees near the power lines at the camp, but found no signs of problems with the black oak, which broke off about 32 feet from the ground, Oliver said. The trunk had a diameter of 53 inches.

"Trees break. It's just nature," he said. "There is nothing specifically wrong with the trees at that camp."

There are no plans to cut short the two-week session at Camp Tawonga, a mainstay for kids from the Bay Area's Jewish community since 1925. But stunned parents spent Wednesday in anguish, mourning the beloved, curly-haired counselor, and poised to sweep up their children if the call came.

In the frantic aftermath of the tree crash, initial reports to Cal Fire set the number of injured at 20 people, but those numbers were later revised downward. Camp leaders said Wednesday that the four injured staff members "are all doing well." Injured counselors Anya Schultz and Juliet Ulibarri were released and headed back to camp Wednesday night; Elizabeth "Lizzie" Moore and Cara Sheedy were still being treated.

The camp's executive director, Ken Kramarz emphasized in an email to parents that emergency responders arrived within minutes, and that the children were being kept safe.

"The children are only aware that a tree fell and that some staff had been injured,'' the camp reported in a second email Wednesday night. "We believe that you, their parents, are best suited to share the sad news that one of the injured staff did not survive.''

On-site staff therapists and grief experts were nearby to help the children sort out what happened.

Campers' parents spent much of Wednesday waiting for word about how their children were coping with the tragedy hours from home at the camp's 160-acre site along the Tuolumne River.

Pediatric oncologist Caroline Hastings of Oakland, whose 11-year-old daughter is at the camp, said she had been contacted by rabbis at two temples in Northern California who offered limited information and assistance. Although she found herself terribly anxious for more news, Hastings said she trusted the camp to complete the session which ends Friday, and handle the children's emotional needs.

"We all have the urge to go up and save our children, but my daughter at age 11 is old enough to understand what happened and find comfort in her friends and the counselors," she said. "There's a lot of important healing that you can do by being all together. Leaving and running away does not allow them to really internalize what happened."

Lisa Fernandez, a former Mercury News staff writer who is now senior digital editor at NBC Bay Area, agreed. Her 7-year-old son and 10-year-old daughter are also at the camp this session, and she said she believes the greatest help to them is not rushing to their rescue.

"I'm perfectly assured knowing that the camp is going to do something appropriate for the kids," Fernandez said. "I'm picturing a really nice, meaningful service with candles and prayers and crying and hugs. I want my kids to be around that tonight."

Lea Kingsbury, who works at a Palo Alto synagogue and has sent two children to camp Tawonga, said she would have a very different response.

"They're in my thoughts and prayers, it's a horrible thing that's happened," Kingsbury said, noting that many counselors are former campers in the tight-knit Camp Tawonga. But "if it were me," she added, "I would rush up there. I would really want to be there for my kids to make sure they're OK."